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The authors regret that the supplementary information of the above article contained a number of errors. The correct and final version follows. The authors would like to apologise for any inconvenience caused.

Floodplains remove nitrate from rivers through denitrification and thus improve water quality. The Danube River Basin (DRB) has been affected by elevated nitrate concentrations and a massive loss of intact floodplains and the ecosystem services they provide. Restoration measures intend to secure and improve these valuable ecosystem services, including nitrate removal. Our study provides the first large-scale estimate of the function of large active floodplains in the DRB to remove riverine nitrate and assesses the contribution of reconnection measures. We applied a nutrient emission model in 6 river systems and coupled it with denitrification and flooding models which we adapted to floodplains. The floodplains have the capacity to eliminate about 33,200 t nitrate-N annually, which corresponds to 6.5 % of the total nitrogen emissions in the DRB. More nitrate is removed in-stream at regular flow conditions than in floodplain soils during floods. However, increasing frequently inundated floodplain areas reveals greater potential for improvement than increasing the channel network. In total, we estimate that 14.5 % more nitrate can be removed in reconnected floodplains. The largest share of nitrogen emissions is retained in the Yantra and Tisza floodplains, where reconnections are expected to have the greatest impact on water quality. In absolute numbers, the floodplains of the lower Danube convert the greatest quantities of nitrate, driven by the high input loads. These estimates are subject to uncertainties due to the heterogeneity of the available input data. Still, our results are within the range of similar studies. Reconnections of large floodplains in the DRB can, thus, make a distinct contribution to improving water quality. A better representation of the spatial configuration of water quality functions and the effect of floodplain reconnections may support the strategic planning of such to achieve multiple benefits and environmental targets.

The progressive loss of biodiversity in rivers and their floodplains has not yet been stopped. With the European Biodiversity Strategy and the goal of restoring at least 25,000 km of free-flowing European rivers by 2030, the first important step has been taken. Now we need to be able to effectively demonstrate a reversal of biodiversity loss as well as the success of urgently needed restoration measures. This special issue presents the results of twelve current river and floodplain restoration and evaluation approaches that have successfully combined hydromorphological restoration measures with interdisciplinary research. We report comprehensively on the challenges and opportunities that river and floodplain restoration can offer to protect the biodiversity and ecosystem functioning of these habitats.

Over the last 40 years, a growing number of restoration projects have been implemented to improve the ecological conditions of highly degraded rivers and their floodplains. Despite considerable investment in these projects, information is still limited about the effectiveness and the success of such river restoration measures, mainly due to a lack of standardised and interdisciplinary assessment approaches. During the project ‘Wilde Mulde – Restoration of a dynamic riverine landscape in Central Germany’, we implemented hydromorphological restoration measures (installation of large wood, removal of rip-rap, reconnection of a former river side-arm) along a lowland river in Central Germany. We carried out intensive scientific monitoring of biodiversity, hydromorphology, ecosystem functions and services, as well as socio-economic aspects. A BACI (Before/After-Control/Impact) design was used to identify the spatial and temporal effects of the restoration measures and to distinguish them from changes caused by background variation. For this, we used a comprehensive set of indicators, including abiotic (flow velocity, diversity of riverbed topography, and flow resistance), biological (ecosystem respiration, macroinvertebrates, fish, carabids, vegetation, and birds) and socio-economic (acceptance and public awareness) indicators as well as the ecosystem service indicator aesthetic quality of the landscape. To meet the inherent challenges of such a large-scale field experiment, like unpredictable environmental conditions, we used an experimental approach that allowed us to demonstrate a measurable success of the implemented restoration measures. The majority of the abiotic and some of the biological and socio-economic indicators at the restored sites approached values of a natural reference site while already deviating from values of a non-natural reference site two years after restoration. In addition to the applied interdisciplinary approach, multiple scales of field inves

Various ecosystem functions provided by floodplains depend on a natural river activity and floodplain morphology. Therefore, anthropogenic alterations of rivers modify their flooding regimes and may affect the provisioning of numerous ecosystem functions. Restoration projects, which aim at reestablishing natural processes of floodplains, require a better understanding of the ecosystem’s ability to simultaneously provide multiple functions (multifunctionality) and how this relates to the environmental template.Here we investigate the relationship between environmental drivers and ecosystem multifunctionality. We focus on 24 ecosystem functions, representing five ecosystem services provided by floodplains of the Mulde River: plant productivity, biodiversity provisioning, retention of sediments, nutrients and pollutants. These functions were measured on 74 plots located on three well preserved floodplain sites of the Mulde River. We described synergies and trade-offs between single functions using correlations and calculated quantitative measures of ecosystem multifunctionality, quantified as the number of functions provided above either 50% of maximal functioning, or 75% of maximal functioning. We then explored relations of multifunctionality with two environmental factors, which also affect the probability of flooding i.e., the hydrological distance and the distance to the water table.Although numerous functions related to sedimentation processes were positively correlated to each other, they traded off with functions related to biodiversity provisioning. This advocates the application of a holistic measure of ecosystem functioning. Multifunctionality indices decreased with an increase of both distance to the water table and hydrological distance, with effects of the distance to the water table being most strongly negative. These findings imply that ecosystem multifunctionality is highest at sites which are flooded regularly. We conclude that restoration attempts whi

Sediment and nutrient retention are essential ecosystem functions that floodplains provide and that improve river water quality. During floods, the floodplain vegetation retains sediment, which settles on plant surfaces and the soil underneath plants. Both sedimentation processes require that flow velocity is reduced, which may be caused by the topographic features and the vegetation structure of the floodplain. However, the relative importance of these two drivers and their key components have rarely been both quantified. In addition to topographic factors, we expect vegetation height and density, mean leaf size and pubescence, as well as species diversity of the floodplain vegetation to increase the floodplain’s capacity for sedimentation. To test this, we measured sediment and nutrients (carbon, nitrogen and phosphorus) both on the vegetation itself and on sediment traps underneath the vegetation after a flood at 24 sites along the River Mulde (Germany). Additionally, we measured biotic and topographic predictor variables. Sedimentation on the vegetation surface was positively driven by plant biomass and the height variation of the vegetation, and decreased with the hydrological distance (total R2 = 0.56). Sedimentation underneath the vegetation was not driven by any vegetation characteristics but decreased with hydrological distance (total R2 = 0.42). Carbon, nitrogen and phosphorus content in the sediment on the traps increased with the total amount of sediment (total R2 = 0.64, 0.62 and 0.84, respectively), while C, N and P on the vegetation additionally increased with hydrological distance (total R2 = 0.80, 0.79 and 0.92, respectively). This offers the potential to promote sediment and especially nutrient retention via vegetation management, such as adapted mowing. The pronounced signal of the hydrological distance to the river emphasises the importance of a laterally connected floodplain with abandoned meanders and morphological depressions. Our study improv

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Kiesbänke, sich verlagernde Ufer, Flussholz und Seitenarme – all das macht einen Wildfluss aus. Die Untere Mulde besitzt in vielen Abschnitten diese Eigenschaften. Sie ist zugleich der größte Fluss im Norddeutschen Tiefland, dessen Ufer nur teilweise verbaut und dessen Flussbett nicht zur Fahrrinne ausgebaggert wurde. Dieser Naturschatz soll mit dem Verbundprojekt „Wilde Mulde“ stärker ins Bewusstsein der Öffentlichkeit rücken. Zudem sollen vier ausgewählte Abschnitte, denen es an Naturnähe fehlt, durch Naturschutzmaßnahmen entwickelt werden. Umfängliche Forschungsarbeiten begleiten das Projekt. In der durch die großen Jahrhunderthochwasser von 2002 und 2013 geprägten Region war der Projektstart aber alles andere als einfach.

Mixing efficiency is the ratio of the net change in potential energy to the energy expended in producing the mixing. Parameterizations of efficiency and of related mixing coefficients are needed to estimate diapycnal diffusivity from measurements of the turbulent dissipation rate. Comparing diffusivities from microstructure profiling with those inferred from the thickening rate of four simultaneous tracer releases has verified, within observational accuracy, 0.2 as the mixing coefficient over a 30-fold range of diapycnal diffusivities. Although some mixing coefficients can be estimated from pycnocline measurements, at present mixing efficiency must be obtained from channel flows, laboratory experiments, and numerical simulations. Reviewing the different approaches demonstrates that estimates and parameterizations for mixing efficiency and coefficients are not converging beyond the at-sea comparisons with tracer releases, leading to recommendations for a community approach to address this important issue.

Naturnahe Flüsse und ihre Auen sind Lebensräume, die einzigartige und essentielle Ökosystemleistungen (ÖSL) bereitstellen. Auen mildern Hochwasserereignisse und halten Sedimente sowie daran gebundene Nähr- und Schadstoffe zurück. Gleichzeitig verfügen sie über einen besonderen Reichtum an Lebensräumen und sinddamit bedeutende Hotspots der biologischen Vielfalt (Scholz et al. 2012). Wesentliche Steuergrößen für dieErhaltung und Förderung von Biodiversität und ÖSL in Flusslandschaften sind eine diverse flussinterne Hydromorphologie und die dynamische Verbindung zwischen Fluss und Aue (Tockner & Stanford 2002).Der Zustand der Fließgewässer und Flussauen in Deutschland ist einer der Indikatoren in der NationalenStrategie zur biologischen Vielfalt (NBS) und gibt Auskunft über die Situation der Flussauen als Lebensraumvon Pflanzen und Tieren (BMU 2010). In der NBS ist verankert, dass bis 2020 Fließgewässer und Auen inihrer Funktion als Lebensraum soweit gesichert werden sollen, dass eine für Deutschland naturraumtypischeVielfalt an Organismen und Biotopen gewährleistet wird. Um diese Zielsetzung umzusetzen, wurde von derBundesregierung ein Förderprogramm initiiert, in dem Umsetzungsprojekte, Kommunikation und Begleitforschung als Verbundprojekte gemeinsam gefördert werden. So verfolgt das Projekt „Wilde Mulde − Revitalisierung einer Wildflusslandschaft in Mitteldeutschland“ das Ziel, die Untere Mulde von Retzau flussabwärts bis zur Mündung bei Dessau-Roßlau an ausgewählten Standorten zu revitalisieren, um die Interaktionen des Flusses mit seinen angrenzenden Auen zu begünstigen.

Submesoscale stirring contributes to the cascade of tracer variance from large to small scales. Multiple nested surveys in the summer Sargasso Sea with tow-yo and autonomous platforms captured submesoscale water-mass variability in the seasonal pycnocline at 20–60-m depths. To filter out internal waves that dominate dynamic signals on these scales, spectra for salinity anomalies on isopycnals were formed. Salinity-gradient spectra are approximately flat with slopes of −0.2 ± 0.2 over horizontal wavelengths of 0.03–10 km. While the two to three realizations presented here might be biased, more representative measurements in the literature are consistent with a nearly flat submesoscale passive tracer gradient spectrum for horizontal wavelengths in excess of 1 km. A review of mechanisms that could be responsible for a flat passive tracer gradient spectrum rules out (i) quasigeostrophic eddy stirring, (ii) atmospheric forcing through a relict submesoscale winter mixed layer structure or nocturnal mixed layer deepening, (iii) a downscale vortical-mode cascade, and (iv) horizontal diffusion because of shear dispersion of diapycnal mixing. Internal-wave horizontal strain appears to be able to explain horizontal wavenumbers of 0.1–7 cycles per kilometer (cpkm) but not the highest resolved wavenumbers (7–30 cpkm). Submesoscale subduction cannot be ruled out at these depths, though previous observations observe a flat spectrum well below subduction depths, so this seems unlikely. Primitive equation numerical modeling suggests that nonquasigeostrophic subinertial horizontal stirring can produce a flat spectrum. The last need not be limited to mode-one interior or surface Rossby wavenumbers of quasigeostrophic theory but may have a broaderband spectrum extending to smaller horizontal scales associated with frontogenesis and frontal instabilities as well as internal waves., United States. Office of Naval Research (Award N00014-09-1-0633)